Technical Field
Embodiments of the subject matter disclosed herein generally relate to an apparatus and method for acquiring data, and more specifically, to a system that uses conventional seismic sensors and a distributed acoustic sensing system for collecting data, for example, inside a borehole.
Discussion of the Background
To extract hydrocarbon fluids (e.g., oil and gas) from a geological formation that is located underground (subsurface), a well needs to be drilled into the earth, either below the water (in a marine environment) or at the earth's surface (land environment). In both situations, various drilling equipment needs to be lowered into the well, most of the times at depths at which the ambient temperatures and pressures are so high that available electronic components are quickly damaged. After the drilling phase, the well is exploited, which means that other type of equipment needs to be installed to allow the hydrocarbon fluids to exit the underground formation. During this production phase, the flow of hydrocarbon fluids needs to be monitored, i.e., measured with various electronic components.
When the hydrocarbon fluid production decreases, there are available methods (e.g., injection of various fluids that promote the flow of hydrocarbon fluids) for enhancing the oil recovery. These methods require different equipment and knowledge of the well.
All these above-discussed methods share the need to monitor the well, to know the various parameters (e.g., temperature, pressure, density, flow, etc.) of the well and its surrounding, so that the appropriate tool can be deployed in the well and the well is appropriately managed.
There are many devices and systems for measuring/monitoring the parameters of the well and/or around the well. The traditional device is a temperature and/or pressure tool, which is attached to a cable and lowered in the well for measuring the temperature and/or pressure. As noted above, the various electronic components that are located in such tools are negatively impacted by the high temperature, which can exceed 170° C., and in some cases can reach 250° C. Thus, the depth at which these traditional tools are deployed is limited, among others, by the temperature inside the well.
Another traditional device that is deployed inside a well is a seismic sensor, e.g., a geophone. Seismic sensors may be deployed, also attached to a cable, inside the well for measuring seismic signals, either associated with micro-seismic events that happen in the earth, or for measuring seismic signals that are generated by a seismic source at the surface, and then reflected from various geophysical formations underground. The micro-seismic events may be generated due to hydraulic fracturing, or to the extraction of hydrocarbon fluid from underground and the subsequent rearranging of the ground. The seismic source is a man-made source specifically designed to generate acoustic signals that propagate to the geophysical formations of interest and the reflected waves are recorded by the seismic sensors for generating an image of these geophysical formations.
In an effort to overcome the weaknesses of the electronic components of the underground sensors, a new technology has recently been introduced to the oil and gas field. This new technology, distributed acoustic sensing (DAS), uses one or more optical fibers for measuring various parameters inside the well. For an introduction to this technology, see U.S. Patent Application Publication No. 2012/0046866. One advantage of the DAS is that the optical fiber can withstand a high temperature environment much better than the existing electronic components. However, this technology has various limitations on its own, e.g., an interpolation process is used to associate the value of a measured parameter with its actual location underground, whereas an actual location of the measured parameter is not that precise compared to the physical location of the seismic sensor tools, the optical fiber is linear and continuous, without dedicated sensing points. Moreover, the step of data processing is difficult, especially since the measurement concerns an optical constraint (and not a direction of movement), which has to be correlated to useful seismic data.
Thus, there is a need for a device and method that overcome the above noted limitations and provide accurate downhole measurements.